Recently, non-contact tracer control devices for tracing a profile of a model by using a non-contact distance detector have been developed, and in this non-contact distance detector, an optical distance detector is used in such a way that it is fixed to the distal end of a tracer head and the distance of the model surface therefrom is detected to thereby provide a tracing. Accordingly, since there is no fear of damage to the model, models made of a soft material can be used, and thus a wider application of the profile machining is expected.
Nevertheless, conventional non-contact tracer control devices have a problem in that the tracing accuracy is lowered at a portion of a model where the angle of inclination is large. Namely, at such a portion, the measurement optical axis of the distance detector becomes almost parallel to the model surface and the spot on the model surface is enlarged and becomes an ellipsoidal shape, thus lowering the resolution of the distance detector and the tracing accuracy. Particularly, in triangulation type distance detectors, a problem sometimes arises in that the measurement optical axis interferes with the model surface, depending on the inclination angle, and thus the measurement becomes impossible.